A. Field of the Invention
The invention generally concerns small molecules and oligomers based on an anthradithiophene core combined with conjugated oligomer side groups comprising Group 16 elements sulfur, selenium, or tellurium, or combinations thereof. These compounds have electron rich and electron deficient regions and can be used in organic electronic applications.
B. Description of Related Art
The search for more efficient and economically viable electronic devices is an ongoing process. This is especially the case for organic electronic applications (e.g., both photovoltaic and non-photovoltaic applications).
While conjugated organic polymers have found widespread use in organic electronic devices including organic light emitting diodes (OLEDs), organic photovoltaics (OPVs) and organic field effect transistors (OFETs), their small molecule/oligomer counterparts have not. One of the reasons for this is that polymers have continuous π-electron systems, and consequent electron-transport properties make them ideal candidates for a variety of electronic devices. Strategic chemical modification of different polymer moieties with varying electron-rich and electron-poor functionalities allows these electron-transporting molecules to be “tuned” for specific applications.
Some of the potential issues with polymeric-based electronic devices, however, are that they are more complicated to make, more difficult to characterize, and more likely to fail (i.e., lack longevity of use) when compared with small-molecule or oligomer-based devices. Despite these issues with polymer-based electronics, the electronics industry continues to implement and develop the use of polymers in electronics to the detriment of small-molecule/oligomer based electronics.
For instance, there are only a handful of small molecules and oligomers that have been demonstrated to lead to moderate-to-high efficiency OPV devices (efficiencies greater than 4%). One of the reasons for this is due to the challenges encountered in designing small molecules and oligomers with both the correct electronic and absorption characteristics and the ability to form nanoscale, phase-segregated, donor-acceptor pairings in the solid state. In terms of the required electronic properties, a suitable band gap is needed for absorption of a broad swath of the solar spectrum, proper alignment of energy levels for charge transfer to the donor or acceptor partner, and suitable (matching) charge carrier mobilities for the balanced transport and extraction of charge from the OPV device.